The present invention relates to a thermoplastic resin composition position or, more particularly, to a thermoplastic resin composition capable of giving various kinds of shaped articles by molding having excellent impact strength as well as heat resistance and surface luster and useful in the fields of electric appliances, automobiles, foodstuff industries, medical technology, miscellaneous daily necessaries and the like.
Among various kinds of thermoplastic resins currently used in the above mentioned applications, copolymers of an aromatic vinyl monomer and an unsaturated dicarboxylic acid anhydride or, in particular, copolymers of styrene and maleic anhydride, referred to as SMA hereinbelow, are superior to other styrene-based synthetic resins in respect of the heat resistance though with some disadvantageously poor mechanical properties including, in particular, the impact strength.
With an object to improve the impact strength of the SMAtype copolymers, a method has been proposed in which the copolymerization of styrene and maleic anhydride is performed in the presence of a rubbery polymer. Though effective in respect of the improved impact strength of the resultant resin product, this method, however, is not free from several disadvantages including the difficulties encountered in the control of the polymerization reaction due to the increase in the viscosity of the polymerization mixture and the poor heat resistance and surface luster of the shaped articles molded of the resin product.
As another approach to the solution of this problem, an attempt has been made to formulate a polymer blend of which simultaneous improvements can be obtained in both respects of the impact strength and heat resistance which otherwise are contradictory to each other (see, for example, Japanese Pat. Kokai No. 50553/1979). A promising polymer blend disclosed so far therein is prepared by blending a SMA with a kind of copolymeric resin of acrylonitrile, butadiene and styrene (referred to as ABS hereinbelow) and a kind of polycarbonate resin. A problem in this type of polymer blend is the insufficient improvement in the impact strength with thermal degradation of the rubbery constituent because the polycarbonate resin can be dispersed uniformly in the blend only by milling at a relatively high temperature.